By horde you mean attack on your compound or a rush of zombies during a mission? Or generally the zombies?
As for the missions I found that you can position survivors with guns in a corner while you keep making circles with one of them far enough that zombies focus on the running survivor but close enough for others to shoot all the zombies down.
Of course the better the guns the better your chances for survival.
And for the compound defense use the best guns(!) you have. They don’t cost any ammo for defense. And if you don’t have any guns or forgot to equip one and end with a melee there is one nice thing:
If your survivor uses cover he can attack any1 close to the obstacle that grants him cover (it works with the concrete block on the street) so you can just hide, hit and run to the other side, repeat.
Hope that’s helpful